The present invention relates to a synthetic staple fiber which permits "100 percent" open end spinning of polyester fiber at high processing speeds. More particularly, the present invention relates to a synthetic fiber having from about 0.08 to about 0.15 weight percent, based on the total weight of the coated fiber, of a primary finish comprising at least one alkyl phosphate ester salt in combination with a second component selected from the group consisting of quaternary trialkyl ethyl ammonium ethosulfate salts and the polyoxyethylene ether esters of C.sub.8 -C.sub.22 fatty acids.
As is well known in the textile arts, the manufacture and subsequent processing of synthetic fibers requires the application of a fiber processing aid (typically termed a "fiber finish" or "finish"). Such fiber finishes are typically aqueous emulsions or solutions comprised of two major constituents, which function as a lubricant and as an artistat, respectively. Depending on the chemical identities of the lubricant and the antistat, an emulsifier may be required as a third major component. Optional or auxiliary constituents include pH control agents, antioxidants, viscosity modifiers, wetting agents, bacteriocides, and anticorrosive agents.
The salts of alkyl phosphate esters have long been recognized as effective antistatic agents in polyester yarn finishes. Generally, the concentration of these alkyl phosphate ester salts does not exceed twenty five percent of the total weight of the finish composition. See, for example, U.S. Pat. No. 3,341,451, which claims a textile processing agent comprising from 5 to 25 percent of a potassium alkyl phosphate ester in which the alkyl radical has from 6 to 10 carbon atoms, from 50 to 90 percent of an organic liquid such as white mineral oil, and from 5 to 25 percent of a blending agent.
The use of greater than 25 weight percent of an anionic antistat in a fiber finish composition typically results in excessive lapping of the rollers on the drawing frame.
Similarly, quaternary trialkyl ethyl ammonium ethosulfate salts have long been recognized as effective antistatic agents in textile fiber finishes. See, for example, U.S. Pat. No. 3,113,956, which discloses the preparation of such salts by heating stoichiometric quantities of a trialkylamine having a long chain alkyl and two short chain alkyl groups with diethyl sulfate in the presence of from 2 to 15 percent triethanolamine.
While these and various other compounds have been proven effective in reducing the static electricity generated by the ever-increasing processing speeds sought by synthetic fiber manufacturers and processors, the advent of "open end spinning" in staple fiber processing created a heretofore unsatisfied need for a superior synthetic staple fiber which not only exhibits superior lubrication and reduction of static electricity, but also permits "100% open end" spinning of polyester staple fiber.
The classical ring spinning method by which discrete staple fibers are manufactured into continuous spun yarn is well-known and may be summarized as sequentially comprising the steps of
(i) opening the baled, compact staple fiber by means of a "picker" machine, thereby forming loose clumps of staple fiber which are subsequently compressed into a loose batting called a "picker lap";
(ii) combing ("carding") the lap so that the discrete staple fibers are substantially parallelized and forming these parallelized staple fibers into a loose continuous strand called a "card sliver";
(iii) combining a plurality of card slivers into a single, more even strand called "drawn sliver" in which the individual staple fibers are drawn into a more parallel relationship by means of a drawing frame;
(iv) further drawing one or several combined drawn sliver strands into a single continuous threadline, termed a "roving", having a minor amount of tensile strength by means of a "roving" machine which imparts twist to the threadline;
(v) drawing and further twisting the roving on a ring spinning machine to produce a "spun yarn".
In the 1970's high speed "open end" spinning machines were commercially introduced which converted "drawn sliver" into spun yarn in a single step, thereby eliminating the need for separate "roving" and "ring spinning" machines. The open end spinning machines offer the advantage of approximately eight fold higher processing speeds than conventional ring spinning machines.
The advantages of open end spinning have been realized in those applications where 100% cotton, blends of polyester and cotton, 100% acrylic, or 100% nylon have been utilized. However, there are several areas where "100% polyester" rather than blends of cotton and polyester are preferred due to the superior toughness, strength and ease of care properties of polyester fiber.
Unfortunately, textile manufacturers have been unable to fully utilize the inherent advantages of open end spinning in the manufacture of "100% polyester" yarns of relatively low modulus and tenacity-at-break. When an open end spinning machine is operated at its normal production speed with 100% polyester sliver, the resultant yarn tends to break frequently, thereby interrupting the continuous operation of the machine. In practice, textile manufacturers have had to operate their open end spinning machines at significantly lower speeds when making such "100% polyester" yarn to avoid the problem of excessive yarn breakage, known as "ends down".
The inventors are aware of few polyester yarns which can be processed at normal speeds on open end spinning machines at an acceptably low ends down. These few yarns uniformly display high modulus and high tenacity-at-break properties, which are not desirable for all textile applications.
The textile manufacturer is faced with other processing considerations in addition to yarn breakage at the open end spinning machines. These include the minimization of static electricity, especially in high speed carding machines. The staple fiber sliver must be capable of running through a drawing frame without adhering to the sets of rollers which form the nips through which the sliver is drawn. Finally, the staple fiber must not leave fiber fragments ("fly") or finish deposits on the working surfaces of the open end spinning machine.
The problem confronting fiber manufacturers is to develop a staple fiber finish which not only permits high speed operation of open end spinning machines when employing 100% polyester of relatively low modulus and tenacity-at-break, but also exhibits acceptable carding and drawing characteristics.
The present invention provides a staple fiber having relatively low modulus and tenacity-at-break which permits acceptable high speed operation of open end spinning machines when processing "100% polyester" sliver, and which also exhibits acceptable carding and drawing characteristics. A solution to the problem of "excessive ends down", which has bedeviled textile manufacturers for over a decade, has finally been provided by the instant invention.